Steel tubes are widely used as pipes for transporting fluid, and steel tubes that are cut to certain lengths are joined to make up a desired pipe system. According to one process of joining two steel tubes, groves are formed in ends of the steel tubes, the grooved ends are held end to end, and the outer circumferential surfaces of the joined ends are welded to each other. Alternatively, flanges or the like are welded to ends of steel tubes, providing flanged steel tubes, and the flanges are fixed to each other by bolts and nuts on site. According to still another joining process, the outer surfaces of ends of tubes are externally threaded, and are joined to each other by a sleeve coupling whose inner surface is internally threaded.
Pipings are often installed at high places. If steel tubes are welded on site, then the welding process is performed on scaffolds. Therefore, the worker needs to take improper postures to weld the entire circumferential surfaces of the tubes, tending to introduce welding irregularities and misalignments and also to cause a spark-induced risk to surroundings. For replacing pipes or changing pipe layouts, it is necessary to cut off the pipes and then weld the pipes again. Such a process is not easy to carry out.
Joining flanged steel tubes can be performed at high places relatively easily because they can be fastened together by bolts and nuts. However, because the flanges need to be welded to the steel tubes in advance, if the flanges are not welded with sufficient accuracy, then a liquid or gas leakage may occur in the piping, or the piping may not be laid in a desired layout.
According to a recent process, flanges are not directly welded to steel tubes, but loose flanges whose inner surfaces are slidable along the outer surfaces of the steel tubes are slid over the steel tubes. Thereafter, a flaring process is performed to bend ends of the steel tubes outwardly into flanges. On site, a gasket is placed between the flaring ends to be joined, and the loose flanges are fastened to each other by bolts and nuts with the flaring ends sandwiched between the loose flanges. This procedure allows the steel tubes to be joined into a piping through only a machining process without need for a welding process.
It has been customary to use a conventional machine tool to perform the flaring operation. The machine tool that has been dedicated for the flaring operation is a steel tube flanging apparatus comprising a single-stage machining head having conical rollers for spreading tube ends through a small angle and a dual-stage machining head having conical rollers for spreading tube ends through a large angle of 90°. Use of the steel tube flanging apparatus has make the flaring operation efficient.
Steel tubes for use as cold and hot water pipings have inner surfaces coated with zinc by hot dip galvanizing. When such steel tubes are flared, the zinc layer is peeled off or pressed and deformed into surface irregularities under the pressing and squeezing forces, resulting in a reduction in the sealing capability of the joined surfaces. Therefore, it has been the customary practice to forcibly remove the zinc layer with a sander or the like to provide smooth surfaces to be joined after the flaring process.
For making the above process efficient, Japanese laid-open patent publication No. H10-146623 discloses a steel tube flanging apparatus having a scraper combined with a dual-stage roller head for grinding the surfaces to be joined at the same time that the tube ends are spread through 90° by the dual-stage roller head. The disclosed steel tube flanging apparatus is effective in greatly improving the process of grinding the surfaces to be joined.
At piping construction sites, the piping plan and the actual layout details often differ from each other, making it necessary to change piping patterns Piping patterns can easily be changed if steel tubes are joined by welding on site. However, if steel tubes are joined by flanges, then they need to be returned to the machining factory where they are corrected or fabricated again. In view of this, there has been a strong demand for the flaring process to be performed on site. However, the conventional flanging apparatus for flaring steel tubes is large and heavy because it is necessary to move the single-stage machining head and the dual-stage machining head to respective positions in front of fixed steel tubes, and hence cannot easily be brought into piping construction sites.
Corrosion-resistant steel tubes have inner and outer surfaces lined with hard vinyl chloride or the like for protecting gas and water supply pipings from corrosion and stray current corrosion. For joining such corrosion-resistant steel tubes, it has been the practice to weld flanges to non-plated ends of the steel tubes and then line the inner and outer surfaces of the steel tubes and portions of the welded flanges. If the corrosion-resistant steel tubes do not match the dimensions at a piping construction site, then the corrosion-resistant steel tubes have to be processed again in the machining factory. If the piping construction site is located at a remote distance from the machining factory, the process of placing the piping has to be interrupted for a few days in order to process and deliver the steel tubes.
If steel tubes are joined by welding, then welding joints are grooved by the manufacturer and then supplied from the manufacturer. However, steel tubes themselves are supplied, not grooved, from the manufacturer, and are subsequently grooved by the user in a factory, with a large-size lathe or manually with a grinder. At a piping construction site, since steel tubes are manually grooved, a long period of time is required to machine the steel tubes and the steel tubes are liable to have an irregular finish.
To solve the above problems, Japanese laid-open patent publication No. 2002-35849 discloses a combined machining equipment for machining a steel tube, which is capable of not only flaring the steel tube, but also forming a branch tube, externally threading the steel tube, peeling a lining off the steel tube, grinding a flared surface, and grooving an end of the steel tube, and a method of machining such a steel tube. This combined machining equipment can solve many of the conventional problems. However, since this combined machining equipment is heavy and cannot easily be moved, it is not easy to use the combined machining equipment on site.
There has also been a need for the formation of flanges and conically spreading portions on ends of steel tubes for use as structural components, rather than pipings. Therefore, apparatus and methods for easily forming such flanges and conically spreading portions have also been in demand.